Blast furnace gas typically has a relatively high carbon monoxide content, e.g., about 20-28%, allowing use as a fuel gas in various types of burners. However, the dust content of blast furnace gas leaving the blast furnace is too high for a stable functioning of the burners, so the dust content of the blast furnace gas must be lowered substantially. This is usually done with a two-step process. In a first step the larger dust particles are separated in a cyclone. In a second step the smaller particles are separated, usually by means of a scrubber in a wet process. Such a wet process requires significant water consumption and produces sludge and waste water, which require further treatment. The water scrubbing treatment also results in a drop of pressure and temperature of the treated blast furnace gas, which reduces its efficiency as a fuel gas in a downstream gas burner.
To overcome the drawbacks of wet gas cleaning processes it has been proposed to filter the gas by means of filter bags, for instance in WO 2010/034791, which also teaches top remove contaminants before filtering. Fresh blast furnace gas typically comprises a number of acidic contaminants, such as hydrogen chloride, hydrogen fluoride, and hydrogen sulfide. In WO 2010/034791 these contaminants are removed by injecting alkaline agents into the gas flow. Other typical contaminants of blast furnace gas include polycyclic aromatic hydrocarbons (PAH), benzene, toluene and xylene (BTX). These can be removed by injecting absorbents into the blast furnace gas flow, e.g., as a mixture with the reagents for neutralizing the acidic contaminants. A problem encountered with injecting such agents in powder form is that the powder should be distributed evenly over the passing gas flow.
U.S. Pat. No. 4,501,599 discloses a dry scrubber for removing pollutants from aluminum production process emissions, using alumina particles. The pressure in such aluminum production process gas is typically sub-atmospheric, so the alumina is sucked into the passing gas flow.